Conventional container coatings may be derived from a thermally curable formulation that includes particles of a thermoplastic material (typically vinyl chloride polymers such as, for example, polyvinylchloride (“PVC”)), in an organic solvent. When these coatings are applied to a substrate and cured, the thermoplastic material can degrade and discolor. Degradation products such as, for example, hydrochloric acid (“HCl”) can attack the substrate. To stabilize the thermoplastic material and reduce degradation, epoxy resins may be added to the coating formulation that typically include polyglycidyl ethers of aromatic polyols such as bisphenol A (often referred to as “BADGE”). Epoxy novolacs and epoxidized linseed oil have also been used as a stabilizer for thermoplastic coating formulations.
Conventional epoxy-containing thermoplastic coating formulations may include small amounts of (1) unreacted bisphenol A (“BPA”) or BADGE and (2) low-molecular-weight components containing BPA or BADGE which, in the food packaging industry, can potentially migrate into packaged foodstuffs over time. Although the balance of scientific evidence available to date does not indicate clearly that traces of these compounds that might be released from existing coatings pose health risks to humans, these compounds are perceived by some people as being potentially harmful to human health. Consequently, there is a desire to reduce or eliminate these compounds from food-contact coatings. However, it has been problematic to formulate thermoplastic coating formulations that exhibit very low or non-detectable levels of mobile forms of these compounds while still retaining the required coating characteristics (e.g., flexibility, adhesion, corrosion resistance, stability, etc.).
Conventional thermoplastic formulations may also include certain tin-containing compounds (e.g., such as tin mercaptans or tin carboxylates) that are also perceived by some people as being undesirable for use in food-contact coatings. Similar to BPA and BADGE, there is also a desire to reduce or eliminate these compounds from food-contact coatings.
Thus, there is a continuing need for improved stabilizer polymers for use in producing coating compositions that include thermoplastic materials such as PVC.